Developmental System Theory is a theoretical reinterpretation of biological phenomena challenging the conventional gene-centered account of development and evolution. In this paper, I focus on Griffiths and Gray’s version of Developmental Systems Theory and I particularly analyze their reconceptualization of inheritance. First, I present their concept of expanded and diffused inheritance; then, I examine and criticize their refusal of the multiple inheritance system model; finally, I present and contrast Griffiths and Gray’s extension of what they call the “causal parity thesis” from development to evolution. I argue that their proposal is an interesting and programmatic philosophical perspective on biological phenomena but, because of their commitment to holism, fails to provide both more heuristic tools for empirical investigation in biology and a more realistic representation of the biological world.